Question

81a^4-1 factorise

what's the answer?

Answer 1

81a^4-1
(9a^2)^2-1^2
(9a^2+1)(9a^2-1)
(9a^2+1){(3a)^2-1^2}
(9a^2+1)(3a+1)(3a-1)
hope that it helps you.